There are numerous methods described in the patent literature which are said to improve the attributes of absorbent paper products. Some back up their conclusions with experimental data; but many present unsubstantiated statements that may need to be taken cum grano salis. Accordingly, making sense of the hodgepodge of art is far more easily accomplished using hindsight, the following collection being assembled and the relevance of many only becoming apparent only after the invention in the application had been made.
U.S. Pat. No. 3,301,746 by Sanford and Sisson, incorporated herein by reference in its entirety, describes a papermaking scheme for enhancing product attributes usually referred to as through air drying or TAD which avoids overall web compression by forming a patterned array of densified regions in the X-Y plane of the sheet to enhance product strength.
U.S. Pat. No. 4,440,597 by Wells and Hensler, incorporated herein by reference in its entirety, describing a method for increasing the stretch of a paper web by operating the forming section of a paper machine faster than the through air dryer section of the paper machine as an improvement to the basic TAD process for improving the attributes of a through-air-dried sheet. As a result of the speed differential, the paper web is inundated into the through air dryer fabric leading to enhanced stretch and absorbency properties in the base sheet and resulting product. This technique is often referred to a fabric creping.
U.S. Pat. No. 3,812,000 by Salvucci and Yiannos incorporated herein by reference in its entirety, disclose a technique for producing a soft tissue by avoiding mechanical compression of an elastomeric containing furnish until the consistency of the web is at least 80% solids. U.S. Pat. No. 3,821,068 by Shaw, incorporated herein by reference in its entirety, discloses a papermaking scheme for producing soft tissue by avoiding mechanical compaction until the sheet has been dried to at least 80% solids.
U.S. Pat. No. 4,533,437 by Curran and Kershaw, incorporated herein by reference in its entirety; U.S. Pat. Nos. 5,591,305 and 5,569,358 by Cameron, all incorporated herein by reference in their entirety, disclose low-batting, high-bulk-generating felt with improved dewatering capabilities.
Fiber and chemicals can be used to modify the attributes of absorbent paper products. For example, U.S. Pat. No. 5,320,710 by Reeves et al., and incorporated herein by reference in its entirety, describes a new furnish combination extracted from the species Funifera of the genus Hesporaloe in the Agavaceae family. This furnish has fibers which are very long and which have very fine geometrical attributes known to enhance towel and tissue performance. U.S. Pat. No. 3,755,220 by Freimark and Schaftlein, incorporated herein by reference in its entirety, describes a debonding scheme for maintaining wet strength while reducing product dry strength—a method said to enhance the handfeel of towel products.
The use of bulking fibers is said to improve the attributes of the final end absorbent paper product. U.S. Pat. No. 3,434,918 by Bernardin, U.S. Pat. No. 4,204,054 by Lesas et al., U.S. Pat. No. 4,431,481 by Drach et al., U.S. Pat. No. 3,819,470 by Shaw et al., and U.S. Pat. No. 5,087,324 by Awofeso et al., disclose the use of bulking fibers in papermaking webs to improve product attributes like thickness, absorbency, and softness. The aforementioned patents are incorporated herein by reference in their entirety.
U.S. Pat. No. 5,348,620 by Hermans et al., and incorporated herein by reference, discusses a high consistency/high temperature fiber treatment-process using a disperser to improve absorbent paper product attributes. U.S. Pat. No. 4,300,981 by Carstens and U.S. Pat. No. 3,994,771 by Morgan et al., incorporated herein in their entirety by reference, discloses using certain species of hardwood like eucalyptus in stratified webs to improve tissue softness.
Even though the patent literature is replete with suggestions of methods said to improve attributes of towel and tissue products, R&D departments are in general unable to provide practical improvements in absorbent paper products merely by choosing one attribute from column A and another from column B as there are innumerable tradeoffs involved. For example, two-ply products are usually more absorbent and softer than comparable one-ply products. These products are usually formed with the Yankee side of each ply of the web facing outwardly, the Yankee side being typically far smoother than the air side of the web. In addition, bending stiffness of a two-ply product with a slip plane can be roughly one fourth that of similar thickness one-ply products without a slip plane. Since strength and basis weight are directly related while softness and strength are inversely related, increasing basis weight while preserving softness can be problematic. However, when basesheet is converted to finished product, there is typically a converting waste variously estimated at around 15% that must be accounted for in determining whether the advantage of two-ply construction is worth the cost, while it is generally understood that paper machines have higher productivity running heavier sheets such as those found in single ply products. Further, the technology used to emboss and marry the two plies can have quite detrimental effects on softness and strength. Further, while chemicals can be used to improve the tactile properties of the web, they often cause detrimental effects of magnitude not easily predicted unerringly in advance. Thus, manufacturers of absorbent paper products continue to spend millions each year to satisfy their continuing need to find new methods to improve these products. In particular there is a need to for improved methods to produce two-ply towel products combining absorbency, softness, thickness and strength attributes which will satisfy the needs of consumers at costs that are acceptable.